A cheetah? A race car? A rocket? All great guesses. All completely wrong. The fastest thing on Earth is something you can't hold in your hand... and understanding it means understanding lightyears, the speed of light, and why space distances break normal numbers.

Dr Matt Agnew runs the ultimate speed race from Usain Bolt all the way to the speed of light, and explains what a lightyear actually is along the way. Spoiler... most adults get it wrong.

What you'll learn:

• Usain Bolt tops out at around 44 kilometres per hour... the slowest in this race by a long way
• A cheetah sprints at 100 to 120 kilometres per hour... basically a furry rocket
• An F1 car reaches around 350 kilometres per hour... blink and it's gone
• NASA's Parker Solar Probe is the fastest human-made object at 690,000 kilometres per hour
• Light travels so fast it feels instant... and in one second it can circle the entire Earth about seven times
• A lightyear isn't time, it's distance... how far light travels in one whole year, about 9.5 trillion kilometres
• The closest star to Earth after our Sun is Proxima Centauri, just 4.2 lightyears away

Key Science Ideas:

• Speed of light: About 300,000 kilometres per second... the ultimate speed limit of the universe
• Lightyear: A unit of distance, not time... how far light travels in one whole year
• Proxima Centauri: The closest star to Earth after our Sun, 4.2 lightyears away
• Parker Solar Probe: NASA's spacecraft and the fastest human-made object ever built
• Astronomical scale: Why scientists need special units like lightyears to measure enormous distances in space

Fun Experiment: The Lightyear Myth Buster

Ask three people in your house or school what a lightyear is. Most will say it's a unit of time. They're wrong... it's distance. Explain that a lightyear is how far light travels in one year, about 9.5 trillion kilometres. You've just done your first myth-busting science experiment, and you didn't need a single piece of equipment.

Why Though? The show for little scientists who love asking big questions. Follow or subscribe so you never miss an episode.

Why Though? The show for little scientists who love asking big questions. Follow or subscribe so you never miss an episode.

Follow Dr Matt Agnew:

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Website: drmattagnew.com

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Have you ever walked outside on a bright sunny day and suddenly sneezed... with no dust, no pepper, no cat fluff anywhere? Just sunshine and a sneeze? There's a real science reason behind it.

Dr Matt Agnew investigates the sun sneeze mystery. What even is a sneeze? Why does bright light trigger one for some people? And why does it run in families?

What you'll learn:

• Sneezing is your body's nose cleaning button... a blast of air that clears anything annoying from your mucous membrane
• When bright sunlight hits your eyes, your brain urgently signals blink and squint
• For about 1 in 4 people, the blink button and the sneeze button sit really close together in the brain... so pressing one accidentally bumps the other
• Scientists call this ACHOO Syndrome... short for Autosomal Dominant Compelling Helio-Ophthalmic Outburst
• Sun sneezing is linked to your genes, which means it can run in families
• Sun sneezes won't hurt you... but stop before the sneeze hits if you're on a bike or crossing the road

Key Science Ideas:

• Mucous membrane: The sticky lining inside your nose that catches dust, germs and anything annoying
• Optic nerve: The nerve that carries signals from your eyes to your brain
• ACHOO Syndrome: The scientific name for sun sneezing... and yes, the acronym was absolutely intentional
• Genes: The instructions inside your body that decide things like eye colour, height, and apparently whether sunshine makes you sneeze
• Reflex: An automatic body response your brain triggers without you choosing it

Fun Experiment: The Family Sun Sneeze Survey Ask everyone in your family whether they sneeze when they look at bright light. Try a torch in a dark room if the sun isn't cooperating. Keep track of who does and who doesn't. If sun sneezing runs in your family, you'll start to see a pattern... and you'll have just conducted your first genetics experiment at the kitchen table.

Why Though? The show for little scientists who love asking big questions. Follow or subscribe so you never miss an episode.

Follow Dr Matt Agnew:

Instagram: instagram.com/drmattagnew

TikTok: tiktok.com/@drmattagnew

YouTube: youtube.com/@whythoughpod

Website: drmattagnew.com

Find Why Though? podcast across the internet and share with your friends!

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Hosted on Acast. See acast.com/privacy for more information.

Here's something nobody tells you. Most of a fart has absolutely no smell. So what's actually making everyone pinch their nose?

Dr Matt Agnew investigates the science of farts. How do smells actually work? What is a fart made of? And why do some foods make the whole situation so much worse?

What you'll learn:

• Smells are tiny invisible particles floating in the air that your olfactory receptors grab and send to your brain
• A fart is gas made by bacteria in your intestines while they break down food
• Most fart gas has absolutely no smell... nitrogen, hydrogen, carbon dioxide, oxygen and even methane are all odourless
• The real culprit is hydrogen sulfide... just 1% of a fart but enough to clear a room
• Foods like beans, eggs, broccoli, brussels sprouts, garlic, onion and cheese all produce more hydrogen sulfide
• Most people fart between 10 and 20 times a day... farts are natural, healthy, and a sign your body is doing its job
• Astronauts on the International Space Station have to think carefully about farts because the gas can be trapped and even flammable

Key Science Ideas:

• Olfactory receptors: The tiny parts inside your nose that detect smell and send signals to your brain
• Bacteria: Tiny living things in your intestines that help break down food... and make gas while doing it
• Hydrogen sulfide: The gas responsible for that rotten egg smell... and basically every bad fart ever
• Intestines: The long tube where food gets broken down after leaving your stomach
• Microbiome: The community of bacteria living inside your body doing useful work every day

Fun Experiment: The Food Fart Tracker Pick two days this week. On day one eat a meal with plenty of broccoli, beans or eggs. On day two eat a meal without any of those. Pay attention to what happens a few hours after each meal. That difference is hydrogen sulfide in action... your gut bacteria working harder on certain foods and producing more of that one very specific gas. Science is everywhere, even when you'd rather it wasn't.

Why Though? The show for little scientists who love asking big questions. Follow or subscribe so you never miss an episode.

Follow Dr Matt Agnew:

Instagram: instagram.com/drmattagnew

TikTok: tiktok.com/@drmattagnew

YouTube: youtube.com/@whythoughpod

Website: drmattagnew.com

Find Why Though? podcast across the internet and share with your friends!

Instagram: instagram.com/whythoughpod

TikTok: tiktok.com/@whythoughpod

Facebook: facebook.com/whythoughpod

Hosted on Acast. See acast.com/privacy for more information.